1. Field of the Invention
The present invention relates to improvements in a light-emitting diode having a light-reflecting layer.
2. Discussion of the Prior Art
Light-emitting diodes (LED) are widely used for optical data communication, and display or indicator devices, for example. Such light-emitting diodes are generally a semiconductor diode consisting of a pn junction formed on a semiconductor substrate by epitaxy, such as liquid phase epitaxy (LIE). An example of this type of light-emitting diode is disclosed in laid-open Publication No. 1-200678 of an unexamined Japanese Patent Application, and shown in FIG. 9. This light-emitting diode, indicated generally at 140, has a light-generating layer for generating an electromagnetic radiation by electroluminescence, a light-emitting surface 126 through which the radiation is emitted externally of the diode, and a light-reflecting layer 142 disposed on one of opposite sides of the light-generating layer which is remote from the light-emitting surface. The light-reflecting layer is adapted to reflect a portion of the radiation generated by the light-generating layer 116, toward the light-emitting surface 126 so that the radiation reflected by the light-reflecting layer 142 is also emitted through the light-emitting surface 126, for improving the light emitting efficiency of the diode 140. In the light-emitting diode 140 provided with the light-reflecting layer 142 as described above, the component of the radiation generated by the light-generating layer 116 which travels in the direction opposite to the direction from the light-generating layer 116 toward the light-emitting surface 126 is reflected by the light-reflecting layer 142, back toward the light-generating layer 116 so that the reflected component is added to the component which is received by the light-emitting surface 126 directly from the light-generating layer 116. Thus, the light-reflecting layer 142 improves the intensity of the light emitted from the light-emitting surface 126, i.e., the light-emitting efficiency of the LED.
The light-reflecting layer 142 incorporated in the known light-emitting diode 140 is a wave interference type light reflector, which most efficiently reflects a wave whose wavelength is the same as a predetermined nominal wavelength of the reflector. Namely, waves whose wavelengths are more or less different from the nominal wavelength are not efficiently reflected by the light-reflecting layer. Accordingly, the conventional light-reflecting layer 142 does not provide an intended increase in the light-emitting efficiency of the light-emitting diode.
Further, it was found that the provision of the light-reflecting layer 142 on the side of the light-generating layer 116 remote from the light-emitting surface 126 to improve the light emitting efficiency as described above may cause periodic irregular variations in the relative spectral intensity of the light emitted from the light-emitting surface 126, as indicated in FIG. 7, which prevents the practical use of the diode provided with the light-reflecting layer 142.